Where to begin...
Toxic lying management. Promises made (bonuses, raises, shares, everything you wanted to hear) that never happened when goals met, there was always something that let them wiggle out.
Crazy hours, even more than you'd expect for a start-up. Easily 50-60 hours a week. No overtime. I worked Christmas night till 4am without so much as a thanks, and quite literally the opposite and then again around new year's.
Company hasn't made a dime and cheaps out on contract hires. Made us deliver the bad news that "their money is coming, we just need this one more feature done by tonight or no one is getting paid because we are done for". Broke my heart and went against my morals.
CEO constantly wasting developers time. If I had a nickel for every 3 hour random story time...
Verbally and mentally abusive. CEO literally yelled(screamed, standing over, etc) at one of his new employees for something that wasn't related to him at all. Dude was physically shaking after and quit a few days later because of it. That was not the only time something similar happened...
Didn't get my entire last paycheck. Every single employee, not just dev, I talked to that worked there never got their whole last paycheck, some didn't get any of it.
Seriously, I could go on but you get the point, stay far away. This business had somehow survived for years before I got there (multiple entire dev team walk outs because of the above) and it will not change. It's unfortunately rotten to the core and I hope someone else picks up the software eventually..
